You can force it to switch to http-01 by adding the --preferred-challenges http-01 option to the certbot command. Once it's successfully obtained a certificate, that preference will be remembered and used again automatically next time that certificate is renewed.
That will soon be true, but it isn't yet. Certbot's nginx plugin still supports the tls-sni-01 challenge as well, for now, as does Let's Encrypt under certain circumstances. In particular, renewals from the same account are allowed to use tls-sni-01, and Certbot still seems to prefer that challenge in that case (if the user hasn't specified a preference).
Of course everyone should switch to http-01 or another challenge as soon as possible. Presumably when Let's Encrypt disables the challenge in February, Certbot's nginx plugin will switch automatically. However that doesn't help you right now, since your tls-sni-01 is not working for some other reason. So you can switch manually instead.
You can report Certbot bugs at Issues · certbot/certbot · GitHub